DEBATING ACCEPTABLE DETAILS

sydthebeat

I would like to use this thread to debate the merits of the new 'acceptable construction details' as issued by the DOE as part of TGD L 2008 and the use of a thermal bridging factor of 0.08.

if you are referring to a detail please title your post with either a clear description of the detail, or the reference number of the detail eg cavity wall flat roof eaves is ref 1-19....

Hopefully this thread can be used to debate both the practicalities and the theories behind each detail with the view of compiling a review to be issued to the DOE.

I will start by merging it with the existing thread on the cavity wall eaves detail 1-09 to 1-14.

What are technicians suggesting to meet the accrediated details at teh eaves in a cavity wall???

slate cavity closers??
proprietory closers??

archtech

Syd
I have been recommending slate cavity closers, however it is been reviewed at present.

sydthebeat

archtech wrote: »

Syd
I have been recommending slate cavity closers, however it is been reviewed at present.

.... on a steep pitch a slate wont work.... according to the details....
most show the first wall tie i whole block below the wall plate...

structure doesnt seem to have been taken into account...
to comply youd need something close to every bloc being strapped down, in my view....

No6

Here in Mayo it dosnt matter what you reccomend they will not build it!!! Some lads are still struggling with the 1991 building regs!!!:D

muffler

No6 wrote: »

Here in Mayo it dosnt matter what you reccomend they will not build it!!! Some lads are still struggling with the 1991 building regs!!!:D

Have to agree. Same here in Donegal.

Poor Uncle Tom

At the moment it's not being done. On the few I insisted on being closed along under the gable ladders they ended casting on a cap.

No6

I think little things like this are goin to be a huge problem in the future, the tradesmen, builders etc are not inclined to change their ways, the clients qill not pay for the level of supervision required, we will specify it as it is in the regulations but then will not get paid to supervise it so it simply will not happen!!! Fun times ahead!!!

Poor Uncle Tom

It will put huge emphasis on the phrase "....no opening up of works took place during the inspection...." on a certificate of compliance.

Actually a certificate of compliance will only be filled with 'If's and should be's' and will only be worth something if a project is completely supervised.

mickdw

That detail showing the inside block continuing a block higher than outer leaf is nonsense. It wont carry the loading involved and is a crazy detail to be proposing.
Apart from going for a 225mm inner leaf, it cant be done.
Isnt there a new insulating closer available? This used with significant insulation fixed to the inside of the wall wouls seem to be a safe detail. there is reported to be air tightness problems relating to insulated slabs though.

archtech

mickdw wrote: »

That detail showing the inside block continuing a block higher than outer leaf is nonsense.

Most timber frame inner leaves are carried higher than the outer leaf so I don't see a major problem there.

mickdw wrote: »

It wont carry the loading involved and is a crazy detail to be proposing[

Last time I checked timber frame of an overall thickness of 90mm had no difficulty in carrying a roof structure, so I can't see a problem with a 100mm conc block.


One potential way of solving the steeper pitch or wider cavity is to put the wall plate on the outer leaf, however this may not work in all cases.

sydthebeat

archtech wrote: »

1. Most timber frame inner leaves are carried higher than the outer leaf so I don't see a major problem there.

2. Last time I checked timber frame of an overall thickness of 90mm had no difficulty in carrying a roof structure, so I can't see a problem with a 100mm conc block.

3.One potential way of solving the steeper pitch or wider cavity is to put the wall plate on the outer leaf, however this may not work in all cases.

1. we are debating this details use in cavity wall situations, TF construction is somewhat different as the whole inner leaf is the structural element while the outer leaf is basically a clad... what do you think in regard to the cavity wall situation...

2. the whole issue is in regard to the twisting effect of the loading on the wall plate and subsequent block courses.... TF are designed to withstand this effect. cavity leafs are excellent in compression but not so good in tension, which is what occurs when twisted...

3. again, this wouldnt really help with the twisting effect.

In general i dont think this is such a huge problem in a standard two storey or single storey build..the triangulation is optimum in these cases......

its only when the ceiling joists are at a remove from the wall plate does the risks increase.... in these cases i think this detail is dodgy and needs to be supplemented and engineered. Perhaps over sized rafters at closer centers will help restrict the bowing action that causes this twist... and then strap the wall plate down very generously (900 c/c ?)...

sydthebeat

EDITED:

sydthebeat

Theres a real problem emerging regarding the laying of the air tightness membrane before the installation of the concrete slabs.

1. the membranes blow off in high winds
2. the membranes tear as the slabs are jostled into position (defeats the purpose)

A few suggestions have been made to counter act this:

1. use a secondary membrane over the first to act as a slipping sheet (may not work)

or my fav
2. use a concrete engineered brick / soap bar over the membrane before the slabs are laid.

this would also be applicable to the external wall insulation detail at this area as well....

any thoughts / comments?

sas

sydthebeat wrote: »

2. use a concrete engineered brick / soap bar over the membrane before the slabs are laid.

this would also be applicable to the external wall insulation detail at this area as well....

any thoughts / comments?

Are you suggesting that this brick is only underneath the part the hollowcore rests on?

How I envisage your suggestion is

1. 215mm block on flat wall stops 1 course short of correct height for hollowcore slab.
2. Membrane is draped over the wall.
3. 100m wide concrete\engineered brick is place on the inner side of the 215mm wall.
4. Hollow Core is placed on top of this 100mm brick.
5. Membrane is wrapped around the end of the hollowcore and back into the building on top of the hollow core.
6. A 100m block on edge is placed to the outside of the 215mm wall.
7. As this is done the 15mm gap (assuming perfect accuracy of course) between teh 100mm block on edge and the brick\hollowcore is filled with mortar.

How am I doing?

sinnerboy

Syd - if managed properly should be ok .

Place membrane on same day as slabs . A generous width say 1000mm - 300 turns down inner wall face - 700mm towards outer .

Then place slabs . Possible risk of tearing ( minor ) where slabs bear down - but thats about it . The important part for no-tear is where the membrane wraps the slab edge .

When blocks are built over - again risk of minor tearing . Once the slab edge part is intact - should be fine

sydthebeat

sas wrote: »

Are you suggesting that this brick is only underneath the part the hollowcore rests on?

How I envisage your suggestion is

1. 215mm block on flat wall stops 1 course short of correct height for hollowcore slab.
2. Membrane is draped over the wall.
3. 100m wide concrete\engineered brick is place on the inner side of the 215mm wall.
4. Hollow Core is placed on top of this 100mm brick.
5. Membrane is wrapped around the end of the hollowcore and back into the building on top of the hollow core.
6. A 100m block on edge is placed to the outside of the 215mm wall.
7. As this is done the 15mm gap (assuming perfect accuracy of course) between teh 100mm block on edge and the brick\hollowcore is filled with mortar.

How am I doing?

yes, make a lot of sense...

obviously the EWI needs some kind of grounding to adhere to so there must be some kind of blockwork here.
If it can be done for a 100mm inner leaf of a cavity wall i cannot see why it cant be done for a 215 EWI situation.

In reality, if this engineered brick is 75mm deep, then a minimum of 100 mm is needed for a drop down suspended ceiling (see below)... this would be the usual case anyway if HRV ducting, 50mm outlet pipes etc are being dropped below the ceiling....

the membrane can be laped upwards towards the wideslab temporarily... then when the plastering is incorporated up to this membrane level, it can be fixed to the plasterwork... therefore a further 25mm needs to be added to teh ceiling drop down to cover this 25mm seal....

comments??

is it possible to plaster over the air tight membrane and form the seal that way??

sydthebeat

sinnerboy wrote: »

1. Possible risk of tearing ( minor ) where slabs bear down - but thats about it . The important part for no-tear is where the membrane wraps the slab edge .

2. When blocks are built over - again risk of minor tearing . Once the slab edge part is intact - should be fine

1. Im not convinced..... discretion may be a better tact and design the risk out. Once slabs are in place then its too late. Surely the seal is at the points where the GF internal wall meets the internal ceiling, and then requiring a full unbroken membrane all the way until the first floor meets the FF wall. When slabs are laid there is a triangular 'gap' between them underneath, which isnt good for continuity if theres any tears...

2. I cannot see much risk of tearing from the preceding block coursing, wet mortar onto the membrane....

sas

sydthebeat wrote: »

is it possible to plaster over the air tight membrane and form the seal that way??

That was how I was lead to believe it's done.

2 approaches

1. The approach recommended by custom solution providers

There is a tape that can be obtained that you use to stick the membrane to the face of the unplastered block. The room side face of the tape is covered in a fleece that allegedly plaster will adhere to.

2. The approach recommended by the PHI to a friend of mine.

Fix the membrane to the block using a strip of expanded metal which is itself fixed to the wall by nailing it through the membrane. You then plaster up to and over the expanded metal.

The gist of the story is that the PHI has no issue with the specialist systems but they also see little need for expensive custom solutions.

sydthebeat

well then that would allow for the membrane to be sealed upwards using the 75mm we have, so no need for a further drop of the ceiling.
Air tightness can also be improved by sealing the suspended ceiling to the plastered wall with mastic (or caulk?)

soldsold

This may just show up my lack of understanding of basic building do's and dont's but here goes...:eek:

Why use engineered bricks/ soap bar? Why not just:


1. 215mm block on flat wall stops 1 course short of correct height for hollowcore slab.
2. Membrane is draped over the wall.
3. 215mm block on flat is placed on top of membrane (mortared in place?).
4. Hollow Core is mortared in place on top of this 215 block.
5. Membrane is wrapped around the end of both the 215 block and hollowcore and back into the building on top of the hollow core.

Am I correct to assume that the engineered brick is needed so you have each block course bonded in with mortar ie block-mortar-block? If so, how do you get away without block-mortar-block bond at the dpc at the base of the wall?

I can see why the above will not work with EWI as there is nothing for the insulation to stick to, but will it work for cavity walls with wet plaster interior finish (ie plaster over the membrane)?

Is the detail you are discussing the same as/ very similar to the "tony tray" at http://www.tonyshouse.info/?

Steve

sydthebeat

soldsold wrote: »

This may just show up my lack of understanding of basic building do's and dont's but here goes...:eek:

Why use engineered bricks/ soap bar? Why not just:


1. 215mm block on flat wall stops 1 course short of correct height for hollowcore slab.
2. Membrane is draped over the wall.
3. 215mm block on flat is placed on top of membrane (mortared in place?).
4. Hollow Core is mortared in place on top of this 215 block.
5. Membrane is wrapped around the end of both the 215 block and hollowcore and back into the building on top of the hollow core.

Am I correct to assume that the engineered brick is needed so you have each block course bonded in with mortar ie block-mortar-block? If so, how do you get away without block-mortar-block bond at the dpc at the base of the wall?

I can see why the above will not work with EWI as there is nothing for the insulation to stick to, but will it work for cavity walls with wet plaster interior finish (ie plaster over the membrane)?

Is the detail you are discussing the same as/ very similar to the "tony tray" at http://www.tonyshouse.info/?

Steve

you are correct steve, the spec above would work fine for a standard cavity wall build.... myself and sas were debating its merits regarding external insulation build....

soldsold

Thanks for the clarification.

Just realised this forum is for Arch. + Technicians...I'll get my coat...

muffler

soldsold wrote: »

Thanks for the clarification.

Just realised this forum is for Arch. + Technicians...I'll get my coat...

Nah, there's no problem posting here if you have a specific problem or query

archtech

Question what methods are you using to advise clients/building contractors of the acceptable details at construction stage

1. redrawing the relevant acceptable detail as part of your construction details
2. making reference on your drawings to the relevant acceptable details publication and including a copy of the relevant details in the construction documentation
3. both of the above
4. or haven't considered it yet I haven't got to that stage with a project

sydthebeat

archtech wrote: »

Question what methods are you using to advise clients/building contractors of the acceptable details at construction stage

1. redrawing the relevant acceptable detail as part of your construction details
2. making reference on your drawings to the relevant acceptable details publication and including a copy of the relevant details in the construction documentation
3. both of the above
4. or haven't considered it yet I haven't got to that stage with a project

Im including appropriate 'acceptable details' in my provisional BER assessment....
Client then has insulation spec, heating spec, window spec, + typical construction details... if they go wrong its plainly their own fault...

sinnerboy

printed off project relevant UK Accredited Details . Unlike the Irish details - there is a box on each detail for the contractor to sign off

They were included in tender docs
They they were included in contract docs

Under threat of no final payment without signed off details - they were signed off

mickdw

in relation to my post re proposed eaves detail with inner 4" Block raised one course higher and supporting the roof without any closer detail

archtech wrote: »

Most timber frame inner leaves are carried higher than the outer leaf so I don't see a major problem there.

Last time I checked timber frame of an overall thickness of 90mm had no difficulty in carrying a roof structure, so I can't see a problem with a 100mm conc block.

If you dont see the difference between a continuous timber structure supporting the roof and a single 4" block on edge supporting the roof, then I hope you are not involved in design of structural elements.
The 4" block in such a detail is unstable and I would bet a large percentage od them would be moved loosened at the joisting stage of the build. It would take practically no force to move these blocks. The idea of supporting the whole roof structure on something as unstable as this to me just says that that detail had no input from anyone from the structural side of things. Its lunacy.
Its not the bearing capacity of the blocks we need to worry about, but the fact the the block is not in a stable position. Compare this to the timber frame structure and we see that it has a continuous element and is tied / braced to provide a stable support for the roof structure. Put simply, the top 225mm of a timber stud wall cannot just topple over and fall away with minimal force

sinnerboy

mickdw wrote: »

The 4" block in such a detail is unstable and I would bet a large percentage od them would be moved loosened at the joisting stage of the build. It would take practically no force to move these blocks. The idea of supporting the whole roof structure on something as unstable as this to me just says that that detail had no input from anyone from the structural side of things. Its lunacy.
Its not the bearing capacity of the blocks we need to worry about, but the fact the the block is not in a stable position. Compare this to the timber frame structure and we see that it has a continuous element and is tied / braced to provide a stable support for the roof structure. Put simply, the top 225mm of a timber stud wall cannot just topple over and fall away with minimal force

Mick - you must be a structural engineer - you sound like one . I keep hearing similar comments from structural engineers . I believe NO consideration was given to structure when these details were compiled .

Another eyebrow raiser is the idea of inserting an insulating material between a stud wall and its connection to the blockwork external wall ( dry lining condition ) . Make sense thermally but .....